Fix the location to create the index.ts file in the get-started examples

[celeron450]

This PR fixes inconsistencies in the index.ts location across the "Get Started" pages.

In several steps (file structure, seed & query, run index.ts), the index.ts file is located in the src directory. However, the "connect" step incorrectly specifies src/db as the directory in which to create index.ts.

This update changes all src/db references to src in the "connect" step, ensuring consistency with the other steps.

See also #460. If src/db is the preferred location, that PR should update the seed & query and run index.ts steps as well.